I am building a smart sprinkler controller using the Spark Core. I connected Spark Core to a saintsmart 8 channel 5V relay. I wanted to drive the 24V solenoid using a step up converter that converts 5V (Spark Core VCC and GND) to 24V. I tested the output voltage and it is a stable 24V. Once I connect the circuit to the relay output and turn on the relay all the 8 relays start to flicker on-off, but when I use a separate power source (12V) to power the solenoids it works well.
What do you think the problem might be?
Another thing, I am testing using the Tinker app, once I connect the Spark Core to power all the 8 relays are powered on, how can I make it by default powered off when connected? I tried different relays and still the same thing. I am driving the relay from VCC and GND on the Spark Core.
Thank you for you help